Coding system



s. 'KUCHINSKY 2,876,350

CODING SYSTEM March 3, 1959 Filed May 26, 1955 2 Sheets-Sheet l SOURCE OF SWITCHING PULSES INPuT FOR SYNCHRONIZING OR CONTROLLlNG SIGNALS f +E I ""E T 0.0. VOLTAGE SUPPLY SWITCHING MAGNETRON 1;- OUTPUT LOAD PULSE BEAM-SWITCHING g PULSE DEVICE GENERATOR- TUBE SELECTOR 5 POWER 7 F g 2 SUP PLY I RT 74 u [4 ET L 2| L-3| L22 H52 23 1&33 24 5; lOi I}; ll [2 l2 I; I33: "2 3 2 EI0 lz ls =O='4I'-'42431'='44 s 52 1 453 zm 5 -EVENGR|DS "ODD GRIDS INVENTOR.

SAUL KUCHINSKY ATTORNEY March 3, 1959 s. KUCHINSKY 2, 6, 5

comma SYSTEM Filed May 26, 1955 2 Sheet;sSheet 2 INTERROGATION TRANSMITTER INVENTOR ATTORNEY --9 OTHER TARGETS POWER SUPPLY Fig. 4

INTERROGATION 0 5 WU H m I G T M R T m KO 7 N W R9 HL C AT wwm .HNU T E A W N q M m m SS! NU 6 IR United States Patent O 2,876,350 CODING SYSTEM Saul Kuchinsky, Phoenixville, Pa., assignor to Burroughs Corporation, Detroit, Mich, a corporation of Michigan Application May 26, 1955, Serial No. 511,283 7 Claims. (Cl. 25027) This invention relates to coding systems using electron discharge devices and in particular to multiple-position switching tubes operating in circuits which can be selectably connected to provide a. wide variety of output signal combinations.

In many applications of encoding techniques security depends upon how immune the code is to being broken. In most cases, it is mostly a matter of time before skilled analysts break a code. The time required to break a code is closely related to the number of possible permutations and combinations among which the coding can be varied and to the pattern of such variations. Hence, a system offering a large number of possible encoding settings has a comparatively high immunity to compromise through breaking the code.

An object of this invention is to provide a novel coding system capable of providing over one thousand possible output combinations. A further object of this invention is to provide an unusually large number of possible output signal combinations in a highly reliable and quickly adjustable manner, yet in a pattern which appears complex and confusing to external observation.

Another object of this invention is to provide a readily changeable output signal level for each position of a magnetron beam switching tube, for widely varying output pulse waveforms from this magnetron beam switch ing tube.

A form of magnetron beam switching tube which is useful in this invention is that disclosed in copending patent application of Sin-Pih Fan et al., Serial No. 370,086, titled Multi-Position Beam Tube, filed July 24, 1953, now Patent No. 2,721,955. Essentially, magnetron beam switching tubes comprise a plurality of compartments arranged concentrically around an elongated cathode with a magnetic field through the tube parallel to the cathode. Each compartment contains one of each type of a plurality of diiferent electrodes.

On a first or smallest radius around the cathode is a plurality of elongated U-shaped electrodes with their convex surface facing the cathode and equally spaced around the cathode. These electrodes are for beam forming and holding and are called spade electrodes. On a larger radius is an equal number of L-shaped target electrodes. One arm of each L shape is arcuate and positioned circumferentially to cover one of the spaces between spade electrodes. The other arm extends inwardly toward an adjacent spade and may even extend into the concave space of that spade. These target electrodes receive the beam current and provide useful output positions. On a radius intermediate between the spades and the targets is an equal number of rod-shaped switching electrodes. These switching electrodes are positioned in line with one side of each spade and near the end of the arcuate arm of each target. This configuration pro vides a plurality of beam receiving compartments, defined by a spade electrode on each side and a switching grid and target across its outer boundary beyond the spade electrodes.

With a positive potential on the electrodes, relative to the cathode, the permeating magnetic field is of a strength which prevents electrons from the cathode reaching the electrodes. The tube then is a diode magnetron, in cut ofi condition. However, if the potential of one of the spade electrodes is lowered to or near to cathode poten' tial, then the axially symmetrical electrical field in the tube is changed and electrons will flow to the low potential spade and into the adjacent compartment on the side of the spade from which the electrons are coming. All of the spade electrodes are connected to a positive voltage supply through resistors of about 100,000 ohms. When a beam is formed and some electrons flow to a spade, this electron current flowing through the resistor lowers the spade potential and enables that spade to hold the beam stably locked in. Most of the electron beam current flows to the adjacent target electrode. The target electrodes also are connected through resistors and other output circuitry to the positive voltage supply.

The switching electrodes normally are biased to a low positive potential. If the switching grid in a compartment holding the beam is lowered suitably in potential, it causes the beam to fan out so some electrons strike the next spade which is the one nearest the switching electrode and defining the other side of the compartment. As with the first-spade, this electron flow lowers the next spades potential and causes the beam to advance into the next compartment.

If all the switching electrodes were in a common connection, then the other switching electrodes would cause the beam to continue advancing until the potential on the switching grids were returned to the positive bias which does not permit the beam to advance. However, the lower potential is applied for a short predetermined period which is just long enough for the beam to advance one compartment for each application or pulse of this switching signal.

Another connection is applicable, where alternate grids are in common connections, i. e. all odd grids in one connection and all even grids in another connection, and a push-pull or balanced switching signal is applied to these connections. When one set of grids are driven to a negative potential to cause the beam to switch, the other set remains at bias potential or are driven to an opposite, positive potential which prevents beam switch ing through the compartments of these switching electrodes. Hence the beam can advance only one compart ment per switching signal before it is prevented from further advancement.

These beam switching tubes can be cut off again by interrupting the circuit to the voltage supply. They also can be cut off by connecting a spade electrode to the voltage supply through a resistor which is too low in ohmic value to enable that spade to develop an adequate drop in potential and hold the beam when the beam is switched to that spades compartment. When the beam reaches that compartment the beam will extinguish and no output current will flow.

In accordance with the features of one embodiment of this invention, a magnetron beam switching tube is ac tuated by a generator of switching signals to provide a separate output at each of its target electrodes in succession. These targets are connected to output pulse selector circuits which determine the output voltage for each position from among a number of possible output levels. These output circuits are readily adjusted to select one of the various levels. With a ten position beam switching tube and two alternate output possibilities for each position 2 (or 1024) different output combinations are available. This number can be increased by Big. 2 is a functional block diagram of an embodiment of'this invention;

Fig. 3 is a partial schematic diagram of connections to a beam switching tube as used in accordance with this invention;

Fig. 4 is a panel layout illustrating one simplified manner for manually setting a plurality of coded output selec'tor connections;

Figs. 5 and 6 are schematic diagrams of different circuit connections for one array of beam tube electrodes.

Referring to Figs. 1, a magnetron beam switching tube is shown in a general circuit in order to show and describe the method of operation of such tubes before examining their particular utilization in this invention. With a positive potential on the electrodes, relative to the cathode K, and with magnetic field B permeating the tube in adirection causing the magnetic flux to flow toward the bbserver, tube 6 normally is in the cut-E region of its diode magnetron characteristic. While the tube is in this condition, no electrons reach the electrodes. If one of the'spade electrodes 50 is lowered in potential to approximately cathode potential by momentarily closing starting switch 71, or applying a negative pulse on terminal'81, the axially symmetrical electrical field is disturbed. Electrons which formerly travelled in closed loops in the space between cathode and spades now follow equipotential lines and are deflected into a compartment adjacent to spade 50. In this manner, a beam is formed as shown in Fig. l, grazing spade 50 and striking target 40. A small fraction of the beams electron current flows to spade 50, but most of this electron current flows to target 40. E lectrons on spade 50 must flow through a resistor R to return to the voltage supply +E This causes a voltage drop which will hold the potential on spade i) down'after switch 71 is released or the negative pulse on terminal 81 has ceased. This lowered potential enables spade 50 to hold the electron beam locked stably on target 40. Switching electrodes such as switching electrode 60are held at a slight positive bias voltage E relative to cathode K, applied through resistors R When at this bias, switching electrode 60 does not interfere with spade 50 holding a beam on target 40. However, if the potential or switching electrode 60 is lowered to cathode potential or lower, it causes the beam to fan out until it strikes spade 51. As with spade 50, the electron how to spade 51 must go through a resistor R generating a voltage drop which lowers the potential of spade 51. This change in the configuration of equipotential lines in the tube causes the beam to advance to where it grazes spade 51 and strikes target 41. Since switching electrode 61 is not on the same connection as switching electrode 60, the beam does not advance any further. It is to be noted that all switching electrodes can be in a single common connection, and beam advancement can be limited to one compartment by limiting the duration of the switching s gnal which lowers the potential of the switching electrodes. With switching grid electrodes in common connections of alternate grids, i. c. all odd grids together and all even grids together, the beam advancement is more positively limited by the voltages applied, as follows:

' The source of switching pulses, 5, can be a flip-flop pulse generator, applying a negative pulse first on, say, lead 70a, and next on lead 7%. When lead 70a and switching electrodes 60, 62 etc., receive a negative pulse, the beam is switched from target 40 to target 41 as described. The alternate switching electrodes 61, 63, etc, are held at positive bias +E which prevents beam advancement through the beam-holding compartments they control; On the next negative pulse, switching electrode 61 causes thebeam to advance to target 42, but the positive bias now on switching electrode 62 prevents any further beam advancement on that switching signal.

7 The switching signals from source 5 also can be a sinusoidal or other push-pull signal, and the same positive control of beam advancement is provided through the common connections of alternate switching electrodes.

With each spade separately connected to the voltage supply through a resistor R each compartment is capable of holding the electron beam stably on its target. However, if it is desired to extinguish the beam at the end of a cycle through the tube, then spade 59 is connected to a resistor R, which is too low in ohmic value to enable the electron flow to spade 59 to lower its potential far enough to enable spade 59 to hold the beam on target 49. As a result, the beam cuts oif. A suitable ohmic value for R, has been found to be in the order of 100,000 ohms, and for R has been found to be in the order of 40,000 ohms. If spade 59 is connected through another resistor R as are the other spades, then the beam will continue to switch around the tubes compartments in response to switching signals from source 5 until the. beam is cut oh" by some other means such as cathode switch being momentarily opened.

Useful output can be taken from each target electrode 40-49 either as a voltage across a load resistor R, or from other well known output coupling circuits, or as a series circuit current.

Referring to Fig. 2, pulse generator 5 drives the beam of magnetron beam switching tube 6 from target to target in a sequential manner. This switching can be at a regular recurrence rate or in a random manner depending on the synchronizing pulses or other signals driving source 5. Power supply 7 provides the various voltages and currents required for stable operation of a magnetron beam switching tube. Supply 7 also provides the reference voltages to which each output is clamped by the output pulse selector 8. This selector can be set to provide a pulse or no pulse on each targets. output circuit, when the beam switches to the successive targets, producing a pulse waveform upon the selectors output circuit which is utilized by load device 9.

In Fig. 3, five of the ten targets of a magnetron beam switching tube are shown connected to diodes, switches, and load resistors of an output selector circuit. Similar circuitry is provided for the remaining target electrodes, spades and switching grids of each position. The remaining positions or arrays of electrodes are omitted in the interest of reducing the complexity of the drawing. The target electrode, spade, and switching grid which form each compartment establish a position in the tube hereafter designated an array of electrodes. Enamining an array here designated the initial array it is seen that target 40 is connected to diodes 20 and 3t), spade. 50 is connected to a voltave supply +13 through resistor R and also connects to starting switch 71, and switching grid 60 is connected to a source of switching pulses through terminal 70. If the switching pulses are of sufiiciently short duration so the beam has time to step only one array per pulse, all grids may be commonly connected. Otherwise, additional circuitry such as a source of balanced or push-pull series of switching pulses is required, with alternate grids in common connections, i. e. all odd grids connected together and all even grids connected together, to provide a balanced switching input circuit. In this manner the switching grid beyond the grid performing a desired switching step has a potential which is of the opposite polarity from that required for continued switching. Accordingly, only at single step occurs. Other arrays are similarly connected, except all odd grids are in one common connection to: one side 70b. of the output circuit for source 5 and. all

even grids' are in another common connection to thewhich can connect to one of two or more potentials. In

the, d lii hawn t connects. he to r nd-.1 r; o

+13,,. A useful value for +E has been found to be about +50 volts.

Diode 30 connects target 40 to an output resistor R; commonly coupled in a similar manner to all the other targets, and thence to voltage supply +E The cathode K of the beam switching tube is connected to the voltage supply at E With the connections as above described, diode 20 is able to clamp the potential of target 40 to zero or +E, when a beam strikes target 40, depending on the position of switch 10. When switch is grounded, diode will clamp target 40 down to zero or ground potential when a beam strikes target 40. When switch 10 is connected to +E target 40 will remain at potential +E whether or not a beam strikes target 40. Thus the output pulse selector switch 10 can be set to give a negative-going pulse at point 74 every time the beam switches to target 40, or can be set to give no pulse. The same selector relationship is provided for switches 11 to 19 and associated targets 41- to 49 respectively. Switching signals applied tocircuit 70 z'1 -70b advances the beam through these positions in succession, once starting switch 71 has been momentarily closed, lowering the potential on spade 50 and forming a beam on target 40. Diodes 3039 minimize interaction between arrays in their outputs on common point 74. With the switches 10 to 13 as shown in Fig. 3, pulse waveform 72 will be generated across resistor R for a periodic switching of the beam from target to target. The contribution from targets 40 to 43 are identified as potentials E10 to E13 respectively. Obviously the remaining arrays of the beam switching tube will either provide a negative-going pulse or remain at +E when the beam strikes their targets, depending on the positions of their switches in the output pulse selector.

While diodes have been shown and described, it is understood that any asymmetrical current conductive device may be employed where diodes are utilized so long as current voltage and impedance limitations are met.

Fig. 4 is a typical arrangement of output selector switches 10 to 19, on a panel marked for positions 0 to 9. Magnetron beam switching tube 6 also is mounted thereon. When a switch is in the down position, output will be at approximately zero potential when the beam strikes the associated array in tube 6. When a switch is in the up position output will be at +E When the beam strikes the associated array. Switch 10 clamps position 0 to ground or zero potential, switch 11 clamps position 1 to +E switch 12 clamps position 2 to ground or zero, and so on as shown in Fig. 4. When the electron beam in tube 6 steps through targets 40, 41, 42, etc., for positions 0, 1, 2, etc. the output pulse waveform 73 will be produced. The portion thereof determined by each position is indicated by the position number.

As shown in Fig. 5, the variable plate resistance of a vacuum tube V can be used in place of a manual switch to clamp target 40 to a lower voltage than +E The anode of diode 20 is connected to the cathode of tube V which is shown as a triode but also may be a multigrid tube. The anode of tube V connects to voltage supply +E and the control grid 76 connects to input terminals for coding pulses which replace manual operation of switch 10 in the determination of gating level on diode 20. A resistor R connects from voltage supply -E to the junction 75 of diode 20 and tube V and resistor R connects from junction 75 to voltage supply 1+E Tube V is normally kept with a zero or slightly positive bias so that its plate resistance is low. This will not mean excessive current because resistor R is of comparatively high ohmic value and will limit current when no beam is on target 40. When the beam does strike target 40, the current rating of tube V is so high and its plate resistance is so low as to maintain the target practically at +E When the control grid 76 receives a negative signal 6 voltage from some suitable control device, such as'interrogation receiver 83 of Fig. 6, the plate resistance -or" tube V (Fig. 5) increases to ohmic values greater than resis' tor R For grid bias voltages in excess of cut-ofl bias, the plate resistance of tube V approaches the open circuit leakage resistance between its-connecting points and the impedance from junction to E, is limited by resistor R Resistors R and R are proportioned so that the beam current of tube 6 will not be cut ofi when tube V; is cut off. Then, when the beam strikes target 40, the target and diode 30 are clamped down to a voltage near ground potential, since point 75 and the anode of diode 20 will be held at a low potential by their connection to resistors R and R This results in establishing a nega tive pulse level at point 74, while the beam is on target 40.

' voltages E,, and -|-'E functions as a voltage divider so that the potential to which diode 20 clamps target 40 will vary directly with the voltage applied to grid 76. In this manner, variable amplitude pulses can be produced when required. R and R can be proportioned so point 75 is at zero or a slightly negative voltage when tube V is 'cut ofi. As tube V is biased to less than cut otL'the volt age on point 75 will rise until at full current through tube V point 75 is at voltage +E These variations in the plate resistance of tube V produce a modulation of the voltage to which diode 20 is clamped. In this respect, tube V can be considered a modulator of the voltage applied to diode 20.

Output pulse selection can be provided in the-output circuit shown in Fig. 6. This circuit also is a modulator. A voltage applied to the control grid of tube V is amplified and applied through a first terminal of the secondary winding of transformer T to diode 20. The other terminal of the secondary winding for transformer T is connected to voltage +E The output of transformer T modulates the voltage on diode 20 about its average value of +E When the voltage across the secondary winding of transformer T drops the potential on diode 20 from +E toward zero, target 40 will be clamped to this lower voltage every time a beam strikes target 40 and electron beam current fiows in this output circuitry. If the period of the voltage 77 applied to the control grid of tube V is long, as shown in Fig. 6, then the number of pulses generated during the positive excursion of volt age 77 will depend on how much oftener the beam switching cycle recurs than does a half cycle of this voltage 77. Because diode 30 will not conduct any appreciable electron current from point 74 toward target 40 and diode 20, the positive half cycle of voltage 77 applied to the targets side of diode 30 does not raise point 74 above E Pi1lses which are synchronized with the impingement of a beam upon target 40 can be applied to the control grid of tube V so transformer T applies negative pulses to diode 20 at the same time as the beam reaches target 40. This would impose rigid synchronization requirements between beam switching signals and output pulse selection signals on the various positions, providing a high order of code security and many complex closely timed code combination possibilities.

For example, as shown in Fig. 6, an intercept receiver 82 could be tuned to the carrier frequency of early warn ing radars and the pulse recurrence frequency .of the radar signal fed into switching pulse generator 5 as a synchronizing signal, causing the switching signals on leads 70a and 70b to advance the electron beam in tube 6 one compartment for each radar pulse, once the beam is formed. Interrogation receiver 83 would respond to proper input signals to apply a negative pulse on terminal 81, forming the beam in tube 6, and 'pulsin'g the tube V5 ier each output circuit of tube, 6. Depending on the position of switch 10, a negative going pulse or no pulse would be produced. If switch is set as shown in Fig. 6, a negative pulse 85 would be provided when the switching of the beam to target 40 coincided with a pulse 84 on V If an unsynchronized pulse 86 were received, no output pulse results, regardless of the position of switch 10, since the beam is not on target 40 at that instant. The pulse Waveform which is fed to interrogation transmitter 87 is determined by the positions of switches 10-19. Proper settings will result in an accurately coded signal in response to an interrogation signal received on receiver 83. In this example, synchronization is easy since both incoming signals come from a single station. When separate parts of a system are used and separate stations provide the respective signals, synchronization becomes more difiicult and its presence proves that each signal is genuine and the stations are synchronized on the same master signal.

What is claimed is:

1. A coding system comprising magnetron beam switching means having a cathode and a multiplicity of arrays with each array having a spade electrode, a beam switching electrode and a target electrode, voltage supply means having a terminal connected to said cathode, resistive current conducting means connecting said spade electrodes to said voltage supply means to enable said spade electrodes to hold a beam stably on their respective target electrodes when the beam is switched thereto, a magnetic field permeating said tube to hold the beam in cut-ofi position with a symmetrically applied electric field between the cathode and the arrays, starting means connected to a spade electrode to lower the potential thereof and form a beam in said tube, output circuit means connected to another terminal of said voltage supply means, first asymmetrically conducting means connecting each target electrode to said output circuit means, a reference potential source differing from that of said voltage supply means, second asymmetrically conducting means connected to each target electrode, said asymmetrically conducting means being oriented to pass beam current, a generator of switching signals connected to said beam switching electrodes to advance the beam from one target to the next target in succession, and output waveform selection means interconnecting said second asymmetrically conducting means selectively to said voltage supply means or to said reference potential source to clamp each target electrode to a corresponding one of two selected voltage levels when a beam is switched to said target electrode.

2. A coding system comprising a normally cut-off magnetron beam switching tube having a cathode and a plurality of arrays with each array having at least a spade electrode and a target electrode, voltage supply means having a terminal connected to said cathode, and including a reference voltage source resistance current conducting means connecting said spade electrodes to said voltage supply means to provide an electrical field in said tube and to enable said spade electrodes to hold a beam stably on their respective target electrodes when the beam is switched thereto, magnetic structure providing a magnetic field permeating said tube to hold it in cut-01f condition when a symmetrical electrical field is applied between the cathode and the arrays, starting means connected to one of said spade electrodes to lower the potential thereof and form a beam in said tube, output circuit means connected to another terminal of said voltage supply means, first asymmetrically current conductive means separately connecting each target electrode to said output circuit means and oriented to pass beam current, second asymmetrically current conducting means connected to each target electrode and oriented to pass beam current, switching means connected to the magnetron beam switching tube to advance thebeamthereof from one target to the next target in succession, andoutputwaveform selection means interconnecting said second asymmetrically current conductive means and said voltage supply means to clamp target electrode to a selected potential from said voltage supply means when a beam is switched to said target electrode.

3. A coding system as defined in claim 2 wherein the output waveform selection means are switching means for selectively connecting said second asymmetrically current conductive means to one of a plurality of voltages.

4. A coding system as defined in claim 2 wherein the output waveform selection means are voltage dividers comprising a first resistor connected between said cathode and said second asymmetrically current conductive means, a second resistor connected between said second asymmetrically current conductive means and said voltage supply means, a variable impedance control device shunting said second resistor, and control means for varying the impedance of said control device to establish the clamping voltage applied to said second asymmetrically current conductive means.

5. A coding system as defined in claim 2 wherein the output waveform selection means are voltage dividers comprising a resistor and a variable impedance control device connecting said second asymmetrically current conductive means to said voltage supply means.

6. A coding system as defined in claim 2 wherein each output waveform selection means is an amplifier including a coupling transformer having a secondary winding interconnecting said second asymmetrically current conductive means with said voltage supply means to vary the potential applied to said second asymmetrically current conductive means.

7. An electron discharge device and system comprising, in combination, a magnetron electron beam switching tube permeated by a magnetic field and having a cathode and a plurality of arrays of electrode elements with each array including at least a spade electrode and a beam receiving target electrode and a beam switching electrode, voltage supply means connected to said cathode and to said spade electrodes and operable to provide an electrical field in the tube for forming and for holding a beam stably on a selected one of the target electrodes, means connecting a source of switching signal pulses to said switching electrodes to cause the beam in the tube to advance from target electrode to target electrode in succession, a common output for the tube having separate circuit leads connected to each target electrode of the tube, a diode gate in each such circuit lead oriented to pass beam current between its respective target electrode and the common output, a second circuit lead connected to each target electrode of the tube, separate sources of two diiferent reference potentials, switch means in each of said second circuit leads selectively operable to connect the same to one or the other of said reference potentials, and a diode gate in each of said second circuit leads oriented to pass beam current impinging on its respective target electrode, said last mentioned diodes being operable to clamp the target electrodes at either of said reference potentials when the electron beam strikes the target electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,461,250 Baily Feb. 8, 1949 2,476,066 Rochester July 12, 1949 2,535,303 Lewis Dec. 26, 1950 2,591,997 Backmark Apr. 8, 1952 2,616,061 Charton Oct. 28, 1952 2,620,454 Skellett Dec. 2, 1952 2,656,485 Page Oct. 20, 1953v 2,658,142 St. John Nov. 3, 1953 2,659,814 Sternback Nov. 17, 1953 2,692,727 Hobbs et al. Oct. 26, 1954 2,706,248 Lindberg et al. Apr. 12, 1955 2,721,955 Fan et al. Oct. 25, 1955 

